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diff --git a/erts/doc/src/communication.xml b/erts/doc/src/communication.xml new file mode 100644 index 0000000000..6049123f6a --- /dev/null +++ b/erts/doc/src/communication.xml @@ -0,0 +1,89 @@ +<?xml version="1.0" encoding="latin1" ?> +<!DOCTYPE chapter SYSTEM "chapter.dtd"> + +<chapter> + <header> + <copyright> + <year>2012</year><year>2012</year> + <holder>Ericsson AB. All Rights Reserved.</holder> + </copyright> + <legalnotice> + The contents of this file are subject to the Erlang Public License, + Version 1.1, (the "License"); you may not use this file except in + compliance with the License. You should have received a copy of the + Erlang Public License along with this software. If not, it can be + retrieved online at http://www.erlang.org/. + + Software distributed under the License is distributed on an "AS IS" + basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See + the License for the specific language governing rights and limitations + under the License. + + </legalnotice> + + <title>Communication in Erlang</title> + <prepared>Rickard Green</prepared> + <responsible></responsible> + <docno></docno> + <approved></approved> + <checked></checked> + <date>2012-12-03</date> + <rev>PA1</rev> + <file>communication.xml</file> + </header> + <p>Communication in Erlang is conceptually performed using + asynchronous signaling. All different executing entities + such as processes, and ports communicate via asynchronous + signals. The most commonly used signal is a message. Other + common signals are exit, link, unlink, monitor, demonitor + signals.</p> + <section> + <title>Passing of Signals</title> + <p>The amount of time that passes between a signal being sent + and the arrival of the signal at the destination is unspecified + but positive. If the receiver has terminated, the signal will + not arrive, but it is possible that it triggers another signal. + For example, a link signal sent to a non-existing process will + trigger an exit signal which will be sent back to where the link + signal originated from. When communicating over the distribution, + signals may be lost if the distribution channel goes down.</p> + <p>The only signal ordering guarantee given is the following. If + an entity sends multiple signals to the same destination entity, + the order will be preserved. That is, if <c>A</c> send + a signal <c>S1</c> to <c>B</c>, and later sends + the signal <c>S2</c> to <c>B</c>, <c>S1</c> is guaranteed not to + arrive after <c>S2</c>.</p> + </section> + <section> + <title>Synchronous Communication</title> + <p>Some communication is synchronous. If broken down into pieces, + a synchronous communication operation, consists of two asynchronous + signals. One request signal and one reply signal. An example of + such a synchronous communication is a call to <c>process_info/2</c> + when the first argument is not <c>self()</c>. The caller will send + an asynchronous signal requesting information, and will then + wait for the reply signal containing the requested information. When + the request signal reaches its destination the destination process + replies with the requested information.</p> + </section> + <section> + <title>Implementation</title> + <p>The implementation of different asynchronous signals in the + VM may vary over time, but the behavior will always respect this + concept of asynchronous signals being passed between entities + as described above.</p> + <p>By inspecting the implementation you might notice that some + specific signal actually gives a stricter guarantee than described + above. It is of vital importance that such knowledge about the + implementation is <em>not</em> used by Erlang code, since the + implementation might change at any time without prior notice.</p> + <p>Some example of major implementation changes:</p> + <list type="bulleted"> + <item>As of ERTS version 5.5.2 exit signals to processes are truly + asynchronously delivered.</item> + <item>As of ERTS version 5.10 all signals from processes to ports + are truly asynchronously delivered.</item> + </list> + </section> +</chapter> + |